Bacillus cereus UW85 suppresses damping-off of alfalfa, a disease caused by oomycete pathogens. Disease suppression is partly due to the production of the antibiotic zwittermicin A. Zwittermicin A is an aminopolyol, representing a novel class of antibiotic, and has a broad target range, inhibiting prokaryotes, fungi, and protists. B. cereus UW85 carries a gene for resistance to zwittermicin A, zmaR, that has no known homologs, and preliminary studies suggest that zmaR inactivates zwittermicin A. Inactivated zwittermicin A has different mobilities on both high voltage paper electrophoresis (HVPE) and TLC, suggesting that it has been modified. Determining exactly how zmaR modifies zwittermicin A is the purpose of this study.